1. Field of the Invention
This invention relates to a system for forming a magnetic film in a magnetic field and more particularly to a magnetic film forming system which comprises a plurality of process chambers, of film forming etc., and transport mechanisms for transporting substrates from one process chamber to another.
2. Description of the Related Art
A conventional inline film forming system is described with reference to FIG. 9. The inline film forming system in FIG. 9 comprises a substrate inlet chamber 2, three process chambers 1a, 1b, and 1c, and a substrate outlet chamber 3 which are linked in order. Sluice valves 8a, 8b, 8c, and 8d are disposed between each of the chambers. Each of the process chambers 1a, 1b, and 1c is provided with a device (not shown) for performing one process such as heating a substrate before film forming, sputtering film forming, ion beam sputtering film forming, or film forming by evaporation. A transport line 5 for transporting a substrate 101 is extended through the substrate inlet chamber 2, process chambers 1a, 1b, and 1c, and substrate outlet chamber 3.
The sequence for forming a film by using the system will be described. First, a substrate 101 on which a film is to be formed is fed into the inlet chamber 2, which is then evacuated by evacuation installation 9a. The process chambers 1a, 1b, and 1c, and the outlet chamber 3 are evacuated by evacuation installations 9b, 9c, 9d, and 9e respectively. After the inlet chamber 2 is evacuated, the separation valve 8a is opened and the transport line 5 is operated to transport the substrate 101 to the process chamber 1a, which has been already evacuated. In the process chamber 1a, predetermined steps such as heating the substrate before film formation and film formation are performed by the processing device installed in the chamber. After the predetermined steps are performed, the separation valve 8b is opened and the substrate 101 is transported to the following process chamber 1b over the transport line 5. Upon completion of processing the substrate 101 in the process chamber 1b, the substrate 101 is transported to the process chamber 1c for further processing. After predetermined processing in the process chamber 1c is complete, the substrate 101 is transported to the outlet chamber 3 from which iti is removed. A large number of substrates 101 can be fed in sequence into the substrate inlet chamber 2 and through the process chambers 1a, 1b, and 1c one after another for processing.
By the way, to form a film whose magnetic orientation is aligned, a film forming method in a magnetic field is used by which a film is formed while magnetic orientation of film particles is being aligned by applying a magnetic field. An example of the film forming system in the related art is given in xe2x80x9cJournal of Vacuum Science and Technology A (Composition distribution and magnetic characteristics of sputtered Permalloy films with substrate angle)xe2x80x9d second series volume 7, number 3, May/June 1989. The article describes a technique in which a permanent magnet is attached to a substrate holder fixed to a film forming system and a substrate is mounted on the substrate holder.
To form a magnetic film in a magnetic field by a conventional inline film forming system, magnetic field generation means is fixed outside or inside a process chamber and a magnetic field is applied to space in the process chamber where a substrate is placed.
For example, the conventional inline system in which magnetic field generation means is attached outside a sputter film forming process chamber will be described with reference to FIG. 7. As shown here, Helmholtz magnetic coils 4a, 4b, 4c, and 4d are disposed outside a process chamber 1d which is provided with a magnetic target 3 and an RF power supply 2 for applying voltage to the magnetic target 3. The Helmholtz magnetic coils 4a, 4b, 4c, and 4d form a magnetic field 6 in a space where a substrate 101 is placed. The substrate 101 is supported by a transport line (not shown). Magnetic sputter particles sputtered from the magnetic target 3 are affected by the magnetic field 6 to form a film magnetically oriented on the substrate 101.
The conventional inline system in which magnetic field generation means is attached inside a sputter film forming process chamber wiil be described with reference to FIG. 8. As shown here, permanent magnets 4e and 4f are disposed at places around a substrate 101 carried in a process chamber 1e. The permanent magnets 4e and 4f are supported by magnetic support means 7 fixed to the process chamber 1e. Since the permanent magnets 4e and 4f form a magnetic field 6 in a space where the substrate 101 is supported by a transport line (not shown), sputter particles sputtered from the magnetic target 3 are affected by the magnetic field 6 to form a film magnetically oriented on the substrate 101.
The conventional film forming system having the magnetic field generation means has the following problem: When a substrate is taken out from the film forming system after a film has been formed, it is placed out of the magnetic field of the magnetic field generation means. Thus, if the substrate is taken out from the film forming system in the state in which it is not completely cooled after the film has been formed, the magnetic orientation of the film is not aligned, degrading the magnetic characteristic. To prevent this inconvenience, the substrate must be left in the film forming system until it is completely cooled after film formation. It takes time until the substrate is completely cooled, substantially lowering the throughput of the system.
To form a magnetic multilayer film by using the conventional inline system having the magnetic field generation means, the following problems occur:
(1) To form a multilayer film, a number of film forming process chambers which differ in film forming source must each be provided with magnetic field generation means. At the time, it is very difficult to completely match all directions of magnetic fields applied to substrates by the magnetic field generation means in the process chambers. This causes orientation of the magnetic film to vary from one layer to another, degrading the magnetic characteristic of the magnetic film. The two main reasons why the directions of the magnetic fields in the process chambers cannot be matched are as follows: First, to completely match the directions of the magnetic fields generated by the magnetic field generation means in the film forming process chambers, the directions of coils and magnets must be matched completely; however, it is technically very difficult to completely match the directions of coils and magnets which are separated from each other and adjustment of the directions requires that the system should be stopped over a long period of time. Second, when a substrate is transported, the substrate turns and its direction will vary.
(2) When the magnetic field generation means is installed outside each film forming process chamber, a magnetic field must be generated within the process chamber, thus large magnetic field generation means needs to be installed, increasing costs.
(3) Process chambers must be located apart from each other to prevent magnetic fields generated by magnetic field generation means in the contiguous process chambers from affecting each other to become uneven magnetic fields. Thus, the line in the system is prolonged compared with a normal inline system having no magnetic field generation means, leading to inconvenient installation of the former system.
(4) When a substrate is transported to the contiguous film forming process chamber after film formation, it is temporarily placed out of magnetic field. Thus, if it is transported to the next process chamber in the state in which the substrate is not completely cooled after film formation, it is cooled out of the magnetic field, and thus the magnetic orientation of the film is not aligned, degrading the magnetic characteristic o f the magnetic material. To prevent this inconvenience, the substrate must be left in the process chamber until it is completely cooled after film formation. It takes time to cool the substrate, substantially lowering the throughput of the line.
Accordingly, it is an object of the invention to provide a film forming system which can form a magnetic film having a high magnetic characteristic by always applying a magnetic field in a constant direction to a substrate in the system.
To this end, according to a first embodiment of the invention, there is provided a magnetic film forming system comprising a vacuum container, a substrate pallet for holding a substrate in the vacuum container and being removable, with the substrate held, from the vacuum container, means for supporting the substrate pallet in the vacuum container, means for forming a film on the substrate, and magnetic field generation means for applying a magnetic field to the substrate. The magnetic field generation means is fixed to the substrate pallet. When the substrate pallet is removed from the vacuum container, the magnetic field generation means is taken out from the vacuum container together with the substrate pallet.
According to a second embodiment of the invention, there is provided a magnetic film forming system comprising a vacuum container, a substrate pallet for holding a substrate, transport means for supporting the substrate pallet in the vacuum container and transporting the substrate pallet, means for forming a film on the substrate, and magnetic field generation means for applying a magnetic field to the substrate. The magnetic field generation means is fixed to the substrate pallet. When the substrate pallet is transported by the transport means, the magnetic field generation means is transported together with the substrate pallet in the vacuum container.
In the magnetic film forming system according to the first embodiment of the invention, a substrate on which a film is formed is retained on the substrate pallet and the substrate together with the substrate pallet can be transported in the vacuum container and taken out therefrom. When a film is formed, the substrate together with the substrate pallet is supported by the support means in the vacuum container. The film forming means forms a film on the substrate on the substrate pallet supported by the support means. The magnetic film generation means applies a magnetic field to the substrate and orients the magnetization direction of a film when it is formed.
In the invention, the magnetic field generation means, which is fixed to the substrate pallet, always applies a magnetic field to the substrate in a constant direction unless the substrate slips off the substrate pallet. Therefore, a magnetic field is always applied to the substrate in a constant direction not only when a film is formed, but also while the substrate pallet is moved in the vacuum container or taken out therefrom. So long as the substrate is held on the substrate pallet, a magnetic field is applied regardless of where the substrate is placed in the vacuum container or whether it is placed inside or outside the vacuum container. Thus, even if the substrate is moved before a film is cooled, film orientation does not vary. Further, since the magnetic field generation means is mounted on the same substrate pallet as the substrate, a magnetic field can be applied at close range. Small magnetic field generation means having a small magnetic field strength can apply a magnetic field efficiently, implementing a small system. Since the magnetic field generation means is taken out from the system together with the substrate pallet, the magnetic field direction can also be adjusted easily.
The magnetic film forming system according to the second embodiment of the invention is provided with means for transporting the substrate pallet in the vacuum container. The vacuum container can also be divided into a number of process chambers. In such an inline film forming system, while a substrate is transported from one chamber to another, a magnetic filed is always applied to the substrate in a constant direction by the magnetic field generation means on the substrate pallet, thus there is no risk of the magnetic field application direction varying slightly between each process chamber. Further, since the magnetic field generation means is mounted on the same substrate pallet as the substrate, a magnetic field can be efficiently applied at close range by small magnetic generation means, implementing a small inline film forming system. Since the magnetic field generation means is taken out from the system together with the substrate pallet, the magnetic field direction can also be adjusted easily even if the inline magnetic film forming system comprises a plurality of process chambers.